1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, an in-plane switching mode liquid crystal display device.
2. Discussion of the Related Art
To solve the problem of viewing angle limitation in twisted nematic LCDs, a multi-domain LCD, such as a two-domain TN LCD (TDTN LCD) and a domain divided TN LCD (DDTN LCD), and a TN LCD including an optical compensation film have ben proposed. In these LCDs, however, a contrast ratio is decreased and a color shift is generated according to a viewing angle.
Further, for the purpose of a wide viewing angle, an in-plane switching mode LCD has also been proposed.
FIG. 1 is a plan view of a unit pixel of a conventional in-plane switching mode active matrix LCD. As shown in the drawing, the LCD comprises a data bus line 1 and a gate bus line 2, in which lines 1 and 2 are arranged perpendicularly and/or horizontally in a matrix on a transparent substrate thereby defining a unit pixel region. A common line 5 is arranged parallel to the gate bus line 2 in the pixel region. A thin film transistor (TFT) is formed adjacent a cross point of the data bus line 1 and the gate bus line 2. A common electrode 11 and a data electrode 19 are formed in the pixel region.
FIG. 2 is a sectional view according to line I-I' of FIG. 1. As shown in the drawing, the TFT includes a gate electrode 10 electrically coupled to the gate bus line 2, a gate insulator 13 on the gate electrode 10, an amorphous silicon (a-Si) semiconductor layer 15 on the gate insulator 13, an n+ a-Si layer 16 on the semiconductor layer 15, and source/drain electrodes 17, 18 which are electrically coupled to the data bus line 1 and the data electrode 19, respectively.
The common electrode 11 is electrically coupled to the common line 5, and the data electrode 19 is electrically coupled to the drain electrode 18. Further, a passivation layer 20 and a first alignment layer (not illustrated) are deposited on the data electrode 19 and the gate insulator 13.
On a second substrate 4, a black matrix 6 is formed to prevent a light leakage around the TFT, the data bus line 1, and the gate bus line 2. A color filter layer 7, an over-coat layer 8, and a second alignment layer (not illustrated) are formed on the black matrix 6 in sequence. Finally, a liquid crystal layer is formed between the first and second alignment layer.
FIG. 3 is a drawing showing a structure of the electrodes driving a liquid crystal according to the conventional in-lane switching mode LCD.
Referring to FIG. 3, when a voltage is applied to the liquid crystal layer, the liquid crystal 30 has an average rotation of 45 degrees by the electric field between the common electrode 111 and the data electrode 119 thereby generating a gray inversion in a rotating direction. In particular, in a gray mode, yellow color is presented at +45 degrees of azimuth angle, and blue color is presented at -45 degrees of azimuth angle to a polarizer P by an optical anisotropy of the liquid crystal.